The proposed research involves the study of chondrocyte metabolism in response to environmental stimuli. We are concerned with the regulation of cell proliferation and matrix synthesis. Proteoglycan and collagen syntheses will be studied in vitro. Both changes in rate of synthesis and changes in the types of collagen and proteoglycan will be determined in response to: 1) nutritional factors, 2) changes in matrix composition, 3) serum factors, 4) rate of cell proliferation. Previous studies have shown 7-fold increases in proteoglycan and collagen syntheses during in vitro culture of rabbit articular cartilage slices. This occurred without significant alteration in the differentiated chondrocyte collagen phenotype. The mechanism of this stimulation is sought as well as the identification of factors that are responsible for the stabilization of the collagen phenotype. Since monolayer culture leads to change in the collagen phenotype, the monolayer and slice culture systems will be compared as a means of identifying these critical factors. Our studies will be expanded from rabbit cartilage to include bovine and human articular cartilage which has been characterized as normal or osteoarthritic. Histochemical, autoradiographic, immunohistochemical, and biochemical analyses will be performed. Collagen typing will be accomplished by purification of radioactive collagen and fractionation of intact chains with CM-cellulose or SDS-electrophoresis. Final characterization will be based on the CNBr peptide maps obtained from isolated collagen chains. Proteoglycans will be characterized according to size and their ability to form native aggregates.